Compiler Explorer

Source code

// Rotate instruction generation test.
#include "stdint.h"

namespace {

// A rotate left simulated with shifts.
inline uint32_t uint32_rol(uint32_t _a, int _sa)
{
	return ( _a << _sa) | (_a >> (32-_sa) );
}

// A rotate right simulated with shifts.
inline uint32_t uint32_ror(uint32_t _a, int _sa)
{
	return ( _a >> _sa) | (_a << (32-_sa) );
}
} // namespace

// Export the local inline functions outside the compilation unit
// so the machine code for them is not elimanted:

uint32_t uint32_do_ror(uint32_t _a, int _sa)
{
    return uint32_ror(_a, _sa);
}

uint32_t uint32_do_rol(uint32_t _a, int _sa)
{
    return uint32_rol(_a, _sa);
}

// A caller for the inline rotate right function to see if the compiler
// will still spot the opportunity to generate a ror machine code instruction
// after inlining and other optimisations may have moved the matching code
// sequence around.
uint32_t sum_many_rors(unsigned numRors)
{
    uint32_t ints[numRors];
    uint32_t sum = 0;
    for(unsigned i = 0 ; i < numRors; ++i)
    {
        sum += uint32_ror(ints[i], i);
    }
    return sum;
}